I have a FFF vulture wing from an earlier project. It's about the right size for my eagle, so I thought I'd put it to good use. I'm worried about finding the right CG. Will the CG for that wing be the same on my eagle as it was on a plane having more plane-like proportions?

If so, I can just mark it where it balances on the other plane, and use that point for balancing the eagle. If anything, that should give me a slightly forward CG, as the other plane has a few degrees AOI, and the eagle will have none.

Does that make sense, or not? I'm thinking it will be a good starting point, but not necessarily the real deal.

The tail incidence will impact the flying as well obviously, but it's a good starting point. My eagle climbed pretty steeply and to the left at WOT when balanced at the recommended CG. At about half throttle, though, it flew very level.

I tested just the eagle wing on my Slow Stick before building the body. The 54 in. eagle wing has very close size and area to the SS wing, and it flew pretty much the same.

The tail incidence will impact the flying as well obviously, but it's a good starting point. My eagle climbed pretty steeply and to the left at WOT when balanced at the recommended CG. At about half throttle, though, it flew very level.

I tested just the eagle wing on my Slow Stick before building the body. The 54 in. eagle wing has very close size and area to the SS wing, and it flew pretty much the same.

Was the optimal CG (relative to the wing) the same on your SS as it was on the eagle? And does your SS have any AOI?

Yes, same CG location (once I got it trimmed), and no, no AOI on either the wing or the horizontal stab on the SS. Video of the flight here.

Thanks Tom, that's good info to have.

My vulture wing has very long wingtip feathers. I put clear tape top and bottom and sealed the edges like a pierogie. Not pretty, but it worked well; actually a very nice wing to fly. I peeled all that tape off today, and it didn't fly nearly as well. I think too much of the airflow under the wing bled through the tip feathers. I might try the clear acetate idea I saw earlier in the thread. That should do the job, and look better than the packing tape.

Your wing probably doesn't have that problem as the tip feathers aren't quite as long.

I'll probably build a new wing for my eagle based on everything I've learned here. I'd like to go with a longer wing and shorter chord, for realism. And I like the 3-layer KF design.

And I think a flat tail would be more realistic, and simpler, which means I need to find some blister pack plastic for an invisible fin.

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My vulture wing has very long wingtip feathers. I put clear tape top and bottom and sealed the edges like a pierogie. Not pretty, but it worked well; actually a very nice wing to fly. I peeled all that tape off today, and it didn't fly nearly as well. I think too much of the airflow under the wing bled through the tip feathers. I might try the clear acetate idea I saw earlier in the thread. That should do the job, and look better than the packing tape.

Your wing probably doesn't have that problem as the tip feathers aren't quite as long.

That's interesting, because I cut my tip feathers deeper than the stock plans called for to get more realism, not only in looks, but also in flight characteristics. The thin, individual, feathers create small tip vortices rather than one big one like a plane's wing, resulting in less drag. The only difference with a real bird like an eagle or vulture is that the tip feather deflections are staggered vertically, which I think makes tham even more effective. I curved all mine up with the same radius for simplicity, but if I built another I'd try to curve the front one's up the most, with less and less toward the wing TE.

I was afraid that longer tip feathers would be more prone to getting snapped off in landings, but I've not found that to be a problem with the tip curve plus dihedral. I did snap three off on my maiden flight when I ejected the battery accidentally. Believe it or not, with no battery on board, the eagle likes to fly inverted with no battery and no control. Mine fluttered down inverted but stable, in small stalls, landing almost flat with only the tip feathers on one wing sustaining any damage! Video here.

I think a mature eagle does have higher aspect wings based on all real bird pictures I D/L'd, so your idea of making them either slightly longer and/or with slightly with less chord should look nice, and probably a more efficient glider with the higher aspect ratio.

My wingtip feathers are a lot longer than yours. It was based on the CADD drawing in the pic below. Perhaps there was a little less drag, but I think there was a lot less lift as well. It seemed like I was flying a much smaller wing, it was less stable in turns, and seemed to tip stall more. Then again, it was a little breezier when I flew with the tape removed, so maybe I just misinterpreted what was happening.

If I build another wing it'll have smaller tip feathers. Or I'll try the clear acetate idea.

I'm about to glue up my fuselage. I plan to add a strip of foam to all the inside joints so I can really round the edges. I'm a little concerned about glue sandability. I've read that mixing PU glue w/ lighweight spackle will do the trick, but I've never tried it. I'll be experimenting tonight.

My wing has very long tip feathers (see CADD screen shot a few posts back). They seem to degrade flight performance. I want to cover them with thin, clear plastic. Should I cover the top or the bottom or both?

Flight Observations:
-- A little unstable - hard to get scale-like flight in a breeze.
-- Lots of power. Flies all day on fast idle.
-- Wind penetration sucks. Wants to stop in a slight breeze.
-- Glide sucks. But that helps me land it in my postage stamp backyard.

Notes for next build:
-- Tail feathers too narrow where they meet the fuse, and too big for the wing (my mods). Scale proportions should work fine, and maybe less drag too.
-- Needs more aileron authority. Loops great but won't roll. Too much dihedral? Too big a vertical stabilizer (invisible).
-- Long tip feathers look good, but add drag and kill lift. Acetate on bottom helps, but next time should either shorten the tip feathers or cover with acetate on top AND bottom.
-- This wing (left-over from another project)was a simple 2 layer FFF w/ a spar sandwiched in between, and sanded to a thin flat bottomed airfoil. Should try the KFM-3 airfoil.
-- Consider mono-block fuse with more scale-like proportions. Might reduce drag and improve glide.

All in all, I'm psyched to have succesfully flown this in my backyard! The neigbors were fooled, and very impressed. A local hawk (or falcon?) did not like my presence. Chased me all the way to the ground. I never saw one up so close. I'll try to get pics next time so I can identify it.